Patent GB-1364288-A (GB)
Title: Method and apparatus for recording and retrieving information
IPC: H01L21/8234
Filed: 1971-08-04
Abstract: 1364288 Data store ENERGY CONVERSION DEVICES Inc 4 Aug 1971 [13 Aug 1970] 36578/71 Heading G4C [Also in Divisions H1 and B6] An Ovonic record of retrievable data is made using a layer of material having two structural conditions, a detectable characteristic whose value is different in the two conditions, and internal biasing forces towards one structural condition and internal inhibitions against the action of the biasing forces, and a catalyst which is capable of changing the biasing forces and/or the inhibitions against those forces by actuating the catalyst in desired regions of the material in order to change the structural condition of those portions thereby to record the data. The memory material is such as to exhibit the ovshinsky effect by being reversibly changeable between a generally disordered amorphous state and a more ordered crystalline state by the application of energy, the two states exhibiting widely different values of at least one physical characteristic, e.g. electrical resistance. Other possible structural conditions are mentioned and the Specification gives a large number of examples of a suitable material. The effect of the catalyst, which may for example be iodine, is to reduce (or increase) the energy required to cause a change of structure. Numerous embodiments are described. Briefly the memory may consist of the memory material 11 deposited on a glass substrate and covered by a mask 12 having openings 13 at selected positions. The memory material is then exposed to iodine vapour through the mask and the structure is heated to cause structure changes where the layer 11 is exposed to the iodine vapour. The mask is then removed and the stored information retrieved using light beams which are dispersed only by the altered regions 14. In a modification of this embodiment the iodine vapour is trapped in contact with the memory material selected regions of which are irradiated with light so as to actuate the catalyst in these regions. The data may be erased by a pulse of energy to evaporate the catalyst followed by rapid cooling to freeze the new structure. In a further embodiment the catalyst is a material which dissociates when irradiated formed in a layer on the memory material. This layer may be on top of the memory material or between it and the substrate. Several electrical embodiments are described, e.g. see Fig. 9. As shown an electrode 26 which includes a catalyst is deposited between the memory layer 27 and substrate 25. Various voltages are applied by means of switches 30, 34, 38 to an electrode 28 to read, write and erase data stored in the memory material. The electrode 28 may be transparent so that recording, &c. may be by means of a combination of light 40 and/or the applied voltages. In another embodiment a system is described briefly for recording etc. using a scanning light beam. In two further embodiments, Figs. 20, 21 (not shown), a printing system is described. The memory material is wrapped around a rotating drum and charge is applied to the drum so that, due to the different resistance of the two structural conditions a charge pattern is built up on the drum. Ink particles are attracted to the charged portions and may by contact, be transferred to a carrier on which they are fixed by heat. The fact that the two structural conditions are wetted to different degrees may be used in printing by applying a pigment to the surface. Parts of the surface retain the pigment and parts do not and the pigment is transferred to a carrier again by contact.